MICR characters are generally printed on checks by commercial check printers, generally including bank routing, account identification and serial numberings. Banks can append this printed information with the amount field. Historically, most MICR characters were printed by offset printing methods using magnetic ink. Today, laser or ion-deposition methods are increasingly being used, by both commercial printers and financial institutions, for writing MICR encoded information.
The MICR encoded information is usually decoded by detecting one of two different magnetic properties of the magnetizable ink: remanance and permeability. The remanance method involves sensing weak voltage signals while scanning MICR character shapes that have been previously magnetized. The second decoding method, also known as the DC-bias method, involves detecting the changes in permeability presented by the MICR character shapes as these character shapes are scanned by the detector.
Trying to read laser-generated indicia using DC biasing techniques has become problematical. Such laser-generated indicia are subject to waveform corruption. That is, the high amplitude, laser-printed MICR signal is subject to clipping.
In order to provide a more foolproof method of reading all types of MICR, the present invention reflects the discovery of a decoding technique that reads MICR signals at two different signal levels: at both high and low gain levels. This improvement allows decoding of large and small signal amplitudes without distortion and clipping.
A “bad read” is a decode that contains a rejected character indicator within the decode string. This rejected character indicator represents raw MICR data that the decoder circuitry was unable to recognize as a valid MICR character. A second MICR read often correctly reads a MICR character rejected on the first pass. In addition to ensuring accurate decoding performance, the inventive method includes apparatus that may be configured to perform a dual pass MICR read. This is possible because the document transport of the printer still has control of the check or other MICR encoded document when it is determined that the initial MICR read was unsuccessful (i.e., when a bad read occurred).